In such a blood pump, the impeller comprising a discoidal body rotatable around an axis of rotation, the body comprising an upper surface, a lower surface and a central passage extending in the direction of the axis of rotation between the upper and lower surface for guiding fluid, in particular blood through the body in axial direction when the body is rotated in a pump chamber of a pump and comprising several blades supported by the upper surface for pumping fluid, in particular blood, when the body is rotated in a pump chamber of a pump and several spiral grooves in the lower surface, each groove having a bottom and two sidewalls and being open in an axial direction, merging into an outer surface of the body and extending from this outer surface to the central passage at least for providing a pumping action of fluid, in particular blood, from the outer surface to the central passage when the body is rotated within a pump chamber of a pump and permanent magnets integrated in the body for driving the impeller by a magnetic field, the magnetic field being generatable by a magnetic drive, for example an electro-magnetic drive positioned on the outside of a pump housing and arranged around the axis of rotation.
The present invention furthermore relates to rotary pumps and, more specifically, to centrifugal rotary blood pumps utilizing hydrodynamic or a combination of hydrodynamic and magnetic bearings for contactless suspension and rotation of such an impeller. This allows wearless pump operation and thus prolonged lifespan.
Mechanical circulatory support with left ventricular assist devices (LVADs) to treat end-stage heart failure has broadly demonstrated beneficial outcomes. For long-term applications, such as destination therapy or prolonged bridge to transplant, fully implantable ventricular assist devices are most suited.
Rotary blood pumps, including centrifugal, axial and mixed flow pumps, have the advantage in their small size while being able to achieve full cardiac support, particularly the newest, 3rd generation devices which are rotary pumps with non-contact suspension of the impeller.
Centrifugal pumps have their optimal hydraulic efficiency at lower rotational speeds than axial or mixed flow pumps. The non-contact suspension techniques, passive and active magnetic as well as hydrodynamic, have each certain advantages and limitations that need to be addressed. Passive magnetic bearings can generate high forces to allow operation at high clearance gaps with lowest implied energy losses; they are also less complicated compared to active magnetic bearings.
However, a full passive magnetic bearing is physically not achievable in blood pumps and hence needs to be combined with a second, different suspension type. Active magnetic bearings can also operate at high clearance gaps but need a sophisticated control and feedback system because of their intrinsic instability, what can result in high energy consumption. Furthermore active magnetic bearings may have the problem of failure of electronic components and/or drift of sensors. They also require additional space for the bearing system components, including electronics, coils and sensors.
Hydrodynamic bearings on the other hand are completely passive and do not require active controllers. They do imply energy consumption, mainly due to the induced viscous flow losses. In principle, they incorporate small clearance gaps to create the pressure build-up, which yields the suspension force on the impeller.
These small clearance gaps however increase the flow resistance and thus reduce the bearing wash out flow. Sufficient and continuous fluid flow paths through the bearing sections are crucial though for the wash out. They can reduce the risk of hemolysis and thrombosis of the blood by reducing the exposure time of the fluid to areas of high shear stress as well as avoiding regions of low flow or flow stagnation.
Hence, by developing more sophisticated bearing designs for impellers in rotary blood pumps that combine sufficient load and momentum capacity with sufficient and continuous wash out flow through the bearing section, the reliability and safety of consistent therapeutic support with rotary blood pumps shall be improved.
The patent application PCT/EP 2012/002722 of the same applicant discloses a centrifugal blood pump comprising a housing having an inlet port, an outlet port and a pump chamber connecting these ports and an impeller located in the pump chamber and rotatable around an axis of rotation being coaxial with the inlet port, the impeller having a central axial opening/passage, communicating with the inlet port, several blades and free spaces between the blades, in particular the free spaces being radially open and communicating with the central axial opening and with the outlet port via a volute surrounding the impeller and a magnetic drive, driving the impeller by a magnetic field interacting with permanent magnets integrated in the impeller and a hydrodynamic bearing by several spiral grooves in a lower surface of the impeller opposite to a mating inner surface of a lower wall of the pump chamber. This pump furthermore uses an impeller of the above-mention kind for propelling blood.
During operation the rotating blades or vanes supported on the upper surface of the impeller are pumping blood from the inlet port through the inner central opening or passage of the impeller body to the outlet port. Besides this first blood flow path a secondary internal flow path exists due to the spiral grooves in the lower surface of the impeller body and the gap between this lower surface and a pump housing that exist during rotation. These grooves are pumping blood from the upper surface via the outer surface of the impeller body to the central passage/opening along the lower surface.
By means of the fact that the grooves of this known impeller body extend from the outer surface to the central passage/opening but end prior to the central opening a rising blood pressure is established near the central opening between the lower surface and a opposed wall of the pump chamber that provides a hydrodynamic contactless suspension of the impeller without any mechanical bearings.
Additionally a contactless radial journal bearing may exist when the impeller is rotated for radial stabilization.
Even though this construction allows contactless suspension of the impeller and a washout effect of blood, there is not enough tilt restoration when accidental shock forces are exerted to the pump. As a consequence there is a risk of touchdown of the rotating impeller within the pump chamber/housing unless other electrical or magnetic tilt restoration mechanisms exist.